Spatially surface ion-aggregated solid polymer electrolyte with robust mechanical properties for lithium metal batteries

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Solid polymer electrolytes (SPEs) show great promise for solid-state lithium batteries, but achieving mechanical robustness and fast interfacial kinetics simultaneously poses critical challenges. Herein, we introduce a spatially surface ion-aggregated SPE (SIA-SPE), featuring a LiTFSI-enriched surface layer with a dense poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) microstructure embedded in a polyethylene (PE) framework, enabled by leveraging the selective solubility of lithium salt and PVDF-HFP in fluoroethylene carbonate and dimethyl formamide co-solvents. The submicron salt-rich surface layer not only enhances lithium-ion transportation but also produces an anion-derived inorganic-rich solid electrolyte interphase with electrochemical stability and fast kinetics. In addition, the PE framework and lithium aluminum titanium phosphate nanofillers confine the crystallization of PVDF-HFP and induce a dense configuration with a β-rich phase. Consequently, the SIA-SPE delivers a remarkable tensile strength of 115 MPa and a high ambient ionic conductivity of 0.75 mS cm −1 . The SIA-SPE achieves a record-breaking performance, with a high critical current density of 10 mA cm −2 in Li||Li symmetric cells, stable cycling of 18000 cycles in Li||LiFePO 4 cells at 1.4 A g −1 , and a high capacity of 149.5 mAh g −1 over 350 cycles (8 mg cm −2 LiFePO 4 loading). Excellent performance in a high-voltage LiNi 0.8 Mn 0.1 Co 0.1 O 2 cathode over 1100 cycles and stable cycling over 1000 cycles in pouch cells further demonstrate its scalability for practical applications.